Method of monitoring control channel in wireless communication system

ABSTRACT

A method of monitoring a control channel in a wireless communication system includes receiving, by a user equipment (UE) from a network, information associated with a discontinuous reception (DRX) period via a radio resource control (RRC) signaling, wherein the DRX period includes a monitored duration and an unmonitored duration; monitoring, by the UE, a downlink control channel during the monitored duration, wherein the downlink control channel is used for a downlink shared channel (DL-SCH); continuing monitoring the downlink control channel if the downlink control channel is successfully decoded by the UE during the monitored duration; and entering a DRX mode upon receiving a command message.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/526,765, filed on Jan. 28, 2010, now U.S. Pat. No. 8,254,323, whichis the National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2008/001479, filed on Mar. 17, 2008, which claimsthe benefit of earlier filing date and right of priority to KoreanApplication No. 10-2007-0081981, filed on Aug. 14, 2007, and also claimsthe benefit of U.S. Provisional Application Ser. Nos. 60/896,250, filedon Mar. 21, 2007, and 60/895,418, filed on Mar. 16, 2007, the contentsof which are all incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to wireless communication, and moreparticularly, to a method of reducing battery consumption of a userequipment in a wireless communication system.

BACKGROUND ART

A conventional wide code division multiple access (WCDMA)-based wirelesscommunication method is a very effective wireless transmission method inwhich voice-based data is transmitted at a low speed and a soft handoveris taken into consideration, but is ineffective when data is transmittedat a high speed in a multi-path fading environment. An evolved-universalmobile telecommunications system (E-UMTS) proposes a downlinktransmission speed of about 100 Mbps. In the E-UMTS, as a multipleaccess technique, orthogonal frequency division multiplexing (OFDM) ismainly concerned in downlink, and a discrete Fourier transform spreadOFDM (DFT-S-OFDM) is mainly concerned in uplink in order to minimize apeak-to-average-power-ratio (PAPR) of a user equipment (UE).

FIG. 1 shows a structure of a wireless communication system. Thewireless communication system may be have a network structure of anE-UMTS. The E-UMTS may be referred to as a long-term evolution (LTE)system. The wireless communication system can be widely deployed toprovide a variety of communication services, such as voices, packetdata, etc.

Referring to FIG. 1, a E-UMTS is classified into an evolved-UMTSterrestrial radio access network (E-UTRAN) and an evolved packet core(EPC). The E-UTRAN includes at least one base station (BS) 20. A userequipment (UE) 10 may be fixed or mobile, and may be referred to asanother terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, etc. The BS 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc. There are one ormore cells within the coverage of the BS 20.

Interfaces for transmitting user traffic or control traffic may be usedbetween the BSs 20. Hereinafter, downlink is defined as communicationfrom the BS 20 to the UE 10, and uplink is defined as communication fromthe UE 10 to the BS 20.

The BS 20 provides the UE 10 with an end-to-end point of a user planeand a control plane. The BSs 20 are interconnected by means of an X2interface, and may have a meshed network structure in which the X2interface always exists between the neighboring BSs 20.

The BSs 20 are also connected by means of an S1 interface to the EPC,more specifically, to an access gateway (aGW) 30. The aGW 30 provides anend-to-end point for a session and mobility management function of theUE 10. The S1 interface may be provided between the BS 20 and the aGW 30so that a plurality of nodes can be interconnected in a many-to-manymanner. The aGW 30 can be classified into a part for processing usertraffic and a part for processing control traffic. In this case, forinter-communication, a new interface may be used between an aGW forprocessing new user traffic and an aGW for processing new controltraffic. The aGW 30 is also referred to as a mobility managemententity/user plane entity (MME/UPE).

Layers of a radio interface protocol between a UE and a network can beclassified into L1 layer (a first layer), L2 layer (a second layer), andL3 layer (a third layer) based on the lower three layers of the opensystem interconnection (OSI) model that is well-known in a communicationsystem. A physical layer belongs to the first layer and provides aninformation transfer service on a physical channel. A radio resourcecontrol (RRC) layer belongs to the third layer and serves to controlradio messages between the UE and the network. The UE and the networkexchange RRC messages via the RRC layer. The RRC layer may be located innetwork nodes (i.e., a BS, an aGW, etc.) in a distributed manner, or maybe located only in the BS or the aGW.

The radio interface protocol horizontally includes a physical layer, adata link layer, and a network layer, and vertically includes a userplane for data information transfer and a control plane for controlsignaling delivery.

FIG. 2 is a diagram showing a control plane of a radio interfaceprotocol. FIG. 3 is a diagram showing a user plane of the radiointerface protocol. In FIGS. 2 and 3, a structure of the radio interfaceprotocol between a UE and an E-UTRAN is based on the third generationpartnership project (3GPP) wireless access network standard.

Referring to FIGS. 2 and 3, a physical layer belonging to a first layerprovides an upper layer with an information transfer service on aphysical channel. The physical layer is coupled with a media accesscontrol (MAC) layer, i.e., an upper layer of the physical layer, via atransport channel. Data is transferred between the MAC layer and thephysical layer on the transport channel. In addition, data istransferred between different physical layers, i.e., between physicallayers of a transmitting side and a receiving side.

The MAC layer in a second layer provides services to a radio linkcontrol (RLC) layer, i.e., an upper layer of the MAC layer, via alogical channel. The RLC layer in the second layer supports reliabledata transfer. Functions of the RLC layer can be implemented as afunction block included in the MAC layer. In this case, as indicated bya dotted line, the RLC layer may not exist.

A packet data convergence protocol (PDCP) belonging to the second layerperforms a header compression function. When transmitting an Internetprotocol (IP) packet such as an IPv4 packet or an IPv6 packet, theheader of the IP packet may contain relatively large and unnecessarycontrol information. The PDCP layer reduces the header size of the IPpacket so as to efficiently transmit the IP packet through a radiointerface.

An RRC layer belonging to a third layer is defined only in the controlplane. The RRC layer serves to control the logical channel, thetransport channel, and the physical channel in association withconfiguration, reconfiguration, and release of radio bearers (RBs). AnRB is a service provided by the second layer for data transmissionbetween the UE and the E-UTRAN. The RB is a logical path provided by thefirst and second layers of the radio protocol to deliver data betweenthe UE and the E-UTRAN. In general, when the RB is established,characteristics of radio protocol layers and channels required toprovide a specific service are defined, and all specific parameters andoperation methods are determined.

A downlink transport channel transmits data from the network to the UE.Examples of the downlink transport channel include a broadcast channel(BCH) for transmitting system information and a down-link shared channel(DL-SCH) for transmitting user traffic or control messages. User trafficof downlink multicast or broadcast services or control messages can betransmitted on the DL-SCH or a downlink multicast channel (MCH). Anuplink transport channel include a random access channel (UL-SCH) fortransmitting user traffic or control messages. A paging channel (PCH)may be provided to deliver paging information.

FIG. 4 shows an example of mapping of logical channels onto physicalchannels in a WCDMA system. The section 6.1 of 3GPP TS 25.211 V6.7.0(2005-12) “Technical Specification Group Radio Access Network; Physicalchannels and mapping of transport channels onto physical channels (FDD)(Release 6)” can be incorporated herein by reference.

Referring to FIG. 4, logical channels are a dedicated channel (DCH), anenhanced dedicated channel (E-DCH), a random access channel (RACH), abroadcast channel (BCH), a forward access channel (FACH), a pagingchannel (PCH), and a high speed downlink shared channel (HS-DSCH). Thelogical channels are mapped to various physical channels.

FIG. 5 shows an example of mapping of logical channels onto physicalchannels in an E-UTRAN. The section 5.3.1 of 3GPP TS 36.300 V0.9.0(2007-03) “Technical Specification Group Radio Access Network; EvolvedUniversal Terrestrial Radio Access (E-UTRA) and Evolved UniversalTerrestrial Radio Access Newark (E-UTRAN); Overall description: Stage 2(Release 8)” can be incorporated herein by reference.

Referring to FIG. 5, downlink transport channels (i.e., a DL-SCH, a PCH,and an MCH) except for a BCH are mapped to a physical downlink sharedchannel (PDSCH). A control channel among downlink physical channels maybe a physical downlink control channel (PDCCH). Comparing FIG. 4 andFIG. 5, unlike the WCDMA system using various physical channels, theE-UTRAN uses only two downlink physical channels, i.e., the PDSCH fortraffic data and the PDCCH for a control signal.

In order to receive the PDSCH, a UE first has to monitor the PDCCH.After successfully decoding the PDSCH, a UE can receive the PDSCH byusing scheduling information included in the PDCCH. However, since thePDCCH is an almost unique control channel, the PDCCH is transmittedevery transmission time interval (TTI). The TTI is a unit of schedulingperformed by a BS. The TTI is defined as a time for transmitting onesub-frame. For example, 1 TTI may be 1 ms.

Unlike the WCDMA system capable of monitoring only a channel designedfor a specific purpose, the UE in the E-UTRAN needs to monitor the PDCCHevery TTI in order to check the scheduling information of the UE.However, when the scheduling information of the UE is checked every TTI,the UE may experience significant battery consumption due to arelatively short TTI length.

DISCLOSURE OF THE INVENTION Technical Problem

A method is sought for monitoring a control channel to reduce batteryconsumption of a user equipment.

Technical Solution

In an aspect, a method of monitoring a control channel in a wirelesscommunication system is provided. The method includes monitoring aphysical downlink control channel (PDCCH) during a monitored duration,wherein the monitored duration is a part of a discontinuous reception(DRX) period, the DRX period specifying the periodic repetition of themonitored duration followed by a non-monitored duration.

In another aspect, a method of monitoring a control channel in awireless communication system is provided. The method includesmonitoring a PDCCH during a monitored duration, wherein the monitoredduration is a part of a DRX period, the DRX period specifying theperiodic repetition of the monitored duration followed by anon-monitored duration, and monitoring the PDCCH during an extendedperiod when the PDCCH is successfully decoded during the monitoredduration.

Advantageous Effects

By monitoring a control channel during a discontinuous reception (DRX)period, battery consumption of a user equipment (UE) can be reduced inan evolved-universal mobile telecommunications system (E-UMTS), and anoperation time of the UE can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of a wireless communication system.

FIG. 2 is a diagram showing a control plane of a radio interfaceprotocol.

FIG. 3 is a diagram showing a user plane of a radio Interface protocol.

FIG. 4 shows an example of mapping of logical channels onto physicalchannels in a wide code division multiple access (WCDMA) system.

FIG. 5 shows an example of mapping of logical channels onto physicalchannels in an evolved-universal mobile telecommunications system(E-UMTS).

FIG. 6 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

FIG. 7 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

FIG. 8 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

FIG. 9 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

FIG. 10 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

FIG. 11 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

FIG. 12 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

FIG. 13 is a block diagram showing constitutional elements of a userequipment.

MODE FOR THE INVENTION

A user equipment (UE) monitors a downlink control channel during amonitored duration which exists for each discontinuous reception (DRX)period. The monitored duration is defined by the number of consecutivetransmission time intervals (TTIs).

Every DRX period, the UE detects whether scheduling information of theUE itself is transmitted on a downlink control channel during a specificchecking period. Upon detecting the scheduling information, the UEreceives data by using the scheduling information.

During the monitored duration, when no scheduling information of the UEis received from a base station (BS), the UE does not monitor thedownlink control channel during the remaining cycles of the DRX period.

When the BS establishes the DRX period of the control channel, every DRXperiod, the UE monitors the control channel only during the monitoredduration, and stops monitoring of the control channel during anon-monitored duration.

When the scheduling information of the UE is detected on the downlinkcontrol channel, that is, when decoding of the downlink control channelis successful, the UE can continuously monitor the downlink controlchannel during an extended period even after the monitored duration isover.

When the scheduling information of the UE is detected on the downlinkcontrol channel, the UE can enter a continuous reception mode. In thecontinuous reception mode, the UE can continuously receive the downlinkcontrol channel until a specific condition is satisfied.

There may be an occasion in which, after the UE enters the continuousreception mode from a discontinuous reception mode, the UE re-enters thediscontinuous reception mode from the continuous mode. This occasion mayoccur when the UE does not detect the scheduling information of the UEon the downlink control channel during a specific time period after theUE enters the continuous reception mode.

Such an occasion may also occur when the UE receives from the BS aninstruction, which allows the UE to enter the discontinuous receptionmode, after the UE enters the continuous reception mode.

When the scheduling information is detected within the monitoredduration, the UE can extend the monitored duration. The UE can monitorthe downlink control channel for the extended time period even if themonitored duration is over.

The downlink control channel may be any one of a paging channel andL1/L2 control channel which delivers information regarding on radioresource allocation. The L1/L2 control channel is also referred to as aphysical downlink control channels (PDCCH). The downlink control channelcarries resource allocation information on which the UE receives data ona downlink shared channel (DL-SCH) or on which the UE transmits data onan uplink shared channel (UL-SCH). The downlink control channel carriesscheduling assignment information of the UE. Scheduling assignment maybe uplink assignment and/or downlink assignment. When the downlinkcontrol channel is successful decoded, the UE can recognize that thescheduling information of the UE is being delivered on the downlinkcontrol channel.

The BS can inform the UE of the information which indicates whether theDRX is configured to monitor the control channel, information on a DRXperiod and a monitored duration, information on an extended period, etc.

The BS can inform the UE of configuration information indicating aminimum possible number of sub-frames (or a time duration) which followan n-th sub-frame and in which the UE has to monitor the downlinkcontrol channel.

The BS can inform the UE of information (i.e., configuration informationof the DRX period) on a repetition period of the monitored duration inwhich the UE monitors the downlink control channel.

The BS may monitor the control channel only during the monitoredduration of the DRX period, and inform the UE of DRX configurationinformation indicating whether to stop monitoring during thenon-monitored duration.

Upon detecting the scheduling information of the UE, the BS can informthe UE of information on an extended period in which the DRX period isinactivated and the downlink control channel is continuously monitored.

Information on the monitored duration or the extended period may berepresented by a sub-frame to which the downlink control channel isallocated. The information on the monitored duration or the extendedperiod may be represented by the number of consecutive sub-frames to bemonitored. Alternatively, the information on the monitored duration orthe extended period may be represented by the number of consecutive TTIsfor monitoring the downlink control channel. For example, the monitoredduration is indicated by only one sub-frame, the UE monitors thedownlink control channel only in the one sub-frame. Therefore, if thereis data or control information to be transmitted to the UE, the BS hasto inform this only on the downlink control channel allocated to thesub-frame belonging to the monitored duration. However, when the systemexperiences power shortage, or when a large amount of data has to betransmitted to another user, the BS has to give up data transmission ofanother user in order to inform the UE of the existence of data. Thatis, when only one sub-frame is included in the monitored duration of theUE, the BS experiences significant limits in utilizing radio resources.Therefore, it is effective to define a plurality of consecutivesub-frames (or a plurality of TTIs) in the monitored duration or theextended period.

FIG. 6 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

Referring to FIG. 6, a DRX period has a length of 7 TTIs, and amonitored duration has a length of 2 TTIs. The remaining cycles of theDRX period, that is, a non-monitored duration, have a length of 7 TTIs.The length of the monitored duration is defined by the number ofconsecutive TTIs. The TTI is a unit of scheduling radio resources. TheTTI is a time required to transmit one sub-frame. At least one PDCCH andat least one physical downlink shared channel (PDSCH) can be allocatedto one sub-frame.

A BS can inform a UE of the length of the monitored duration. Themonitored duration is a part of the DRX period. The DRX period specifiesperiodic repetition of the monitored duration followed by thenon-monitored duration.

Every DRX period, the UE monitors at least one PDCCH during themonitored duration. The PDCCH is a control channel carrying schedulingassignment (e.g., uplink assignment or downlink assignment). If decodingis not successfully performed on the PDCCH during the monitoredduration, the UE stops the monitoring of the PDCCH during thenon-monitored duration. The BS can inform the UE of information (i.e.,DRX configuration) indicating whether the PDCCH is monitored during thenon-monitored duration.

The UE monitors the PDCCH during the monitored duration. The UE may wakeup only during the monitored duration to perform uplink transmission ordownlink transmission. For example, the UE may periodically report achannel quality indicator (CQI) to the BS during the monitored duration.

FIG. 7 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

Referring to FIG. 7, every DRX period, a UE monitors a PDCCH during amonitored duration. When decoding is successfully performed on the PDCCHduring the monitored duration, that is, when data to be transmitted tothe UE is detected, data on a DL-SCH is received by using informationindicated on the PDCCH.

When the UE successfully receives the PDCCH on which uplink assignmentor downlink assignment is indicated during the monitored duration, thePDCCH can be monitored during an extended period. In this example, datais indicated at 2 TTIs, and the monitored duration is further extended.If the PDCCH is not successfully decoded during the extended period, theUE re-enters the DRX period. The BS can inform the UE of information onthe extended period. In particular, if there is scheduling informationfor the UE is found, the UE enters a non-DRX mode (i.e., continuousreception mode) during which discontinuous reception (DRX) isinactivated. Further, the UE may continue to monitor the PDCCH until acommand message is received. Upon receiving the command message, the UEenters a DRX mode (i.e., discontinuous reception mode) during whichdiscontinuous reception (DRX) is activated and the DRX period isapplied. Alternatively, the UE may continue to monitor the PDCCH while atimer is running.

FIG. 8 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

Referring to FIG. 8, a DRX period is divided into an on-period and anoff-period. The on-period is a period in which a UE monitors a PDCCH.The off-period is a period in which the UE stops monitoring the PDCCHand enters DRX sleep mode. A BS can inform the UE of information on theon-period or the off-period. When the UE successfully receives the PDCCHduring the off-period, downlink data can be received on a DL-SCH.

The on-period is defined by the number of consecutive TTIs. Theoff-period may also be defined by the number of consecutive TTIs.

The on-period and the off-period may have fixed lengths. That is, duringthe on-period, the UE may do not change the length of the on-period orthe off-period even if scheduling information is detected on the PDCCH.In this case, the on-period and the off-period of the UE have invariablelengths. Therefore, when the on-period is over, the UE transitions tothe off-period regardless of whether transmission information isreceived during the on-period. That, is, although the PDCCH has beensuccessfully received at the first 2 TTIs, the UE does not monitor thePDCCH during the off-period, starting from a time point when theoff-period begins.

FIG. 9 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

Referring to FIG. 9, a BS instructs a UE to skip an off-period, during aspecific DRX period. Scheduling information may not be received within aprevious on-period due to a large amount of data or control informationto be sent from the BS to the UE. In this case, it can be instructedsuch that the off-period of the specific DRX period is skipped duringthe specific DRX period, and thus a current mode can be switched to acontinuous reception mode only during the specific DRX period.Alternatively, in this case, it can be instructed such that the UEswitches the current mode to continuously receive data by stopping DRXconfiguration. When the instruction for skipping the off-period isreceived, the UE does not enter the off-period and performs an operationin the on-period amounting to the skipped periods of time.

FIG. 10 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

Referring to FIG. 10, when a PDCCH is successfully decoded during anon-period of a specific DRX period, the PDCCH can be further monitoredfor a time period amounting to an extended period. The extended periodis defined by the number of consecutive TTIs for monitoring the PDCCHwhen downlink transmission is expected. Herein, the PDCCH issuccessfully decoded during an on-period having a length of 2 TTIs, andthe PDCCH is monitored during an extended period having a length of 2TTIs. Therefore, a total length of the monitored duration is 4 TTIs.

While receiving the downlink control channel during the on-period, whenscheduling assignment (e.g., downlink assignment or uplink assignment)of the UE is detected on the downlink control channel, the UE furthermonitors the PDCCH for a time period amounting to the extended period.If the PDCCH is not successfully decoded during the extended period, theUE re-enters the DRX period.

The BS can instruct the UE to switch to a continuous reception modecontinuously during an on-period in a next DRX period, or switch to thecontinuous reception mode only during several DRX periods, or extends alength of the on-period. Even after the UE switches to the continuousreception mode, the BS can instruct the UE to transition to theoff-period. While staying in the continuous reception mode, when the BSinstructs the UE to transition to the off-period, the UE ends thecontinuous reception mode and transitions to the off-period.

FIG. 11 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

Referring to FIG. 11, when a PDCCH is successfully decoded during anon-period, a UE inactivates an off-period, and further monitors thePDCCH for a time period amounting to an extended period. A BS caninstruct the UE to transition to the off-period during the extendedperiod. That is, the UE can enter a DRX period directly under theinstruction of the BS instead of entering the DRX period after theextended period is over.

FIG. 12 shows an example of a method of monitoring a control channelaccording to an embodiment of the present invention.

Referring to FIG. 12, when data is indicated, a plurality of extendedperiods exist. That is, when a PDCCH is successfully decoded during anon-period, a UE further monitors the PDCCH during an extended period. Ifthe PDCCH is successfully decoded only during the extended period, theUE continuously monitors the PDCCH during an additionally extendedperiod. When data is indicated during an on-period, the PDCCH can becontinuously monitored during a plurality of extended periods after theon-period of a corresponding DRX period is over.

After receiving the data indication, the UE continuously monitors thePDCCH during the extended period in order to receive subsequent downlinktransmission. When data indication is received again, the UEcontinuously monitors again the PDCCH during another extension period.If existence of data is no longer indicated during the additionalextension period, the UE re-enters the DRX period.

Although the control channel is transmitted at a relatively shorttransmission period, the UE monitors the control channel only during theon-period and does not monitor the control channel during theoff-period. The BS can inform the UE of DRX configuration by using amedia access control (MAC) message or a radio resource control (RRC)message. When the control channel is monitored by using a DRX method,battery consumption of the UE can be reduced.

FIG. 13 is a block diagram showing constitutional elements of a UE. A UE50 includes a processor 51, a memory 52, a radio frequency (RF) unit 53,a display unit 54, and a user interface unit 55. The memory 52 iscoupled to the processor 51 and stored an operating system,applications, and general files. The display unit 54 displays a varietyof information of the UE 50 and may use a well-known element such as aliquid crystal display (LCD), an organic light emitting diode (OLED),etc. The user interface unit 55 can be configured with a combination ofwell-known user interfaces such as a keypad, a touch screen, etc. The RFunit 53 is coupled to the processor 51 and transmits and/or receivesradio signals.

Layers of the radio interface protocol are implemented in the processor51. The processor 51 provides a control plane and a user plane. Amonitoring function of the control channel can be implemented in theprocessor 51.

The steps of a method described in connection with the embodimentsdisclosed herein may be implemented by hardware, software or acombination thereof. The hardware may be implemented by an applicationspecific integrated circuit (ASIC) that is designed to perform the abovefunction, a digital signal processing (DSP), a programmable logic device(PLD), a field programmable gate array (FPGA), a processor, acontroller, a microprocessor, the other electronic unit, or acombination thereof. A module for performing the above function mayimplement the software. The software may be stored in a memory unit andexecuted by a processor. The memory unit or the processor may employ avariety of means that is well known to those skilled in the art.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims. Therefore, allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are intended to beembraced by the appended claims.

What is claimed is:
 1. A method of monitoring a control channel in awireless communication system, the method comprising: receiving, by auser equipment (UE) from a network, information associated with adiscontinuous reception (DRX) period via a radio resource control (RRC)signaling, wherein the DRX period includes a monitored duration and anunmonitored duration; monitoring, by the UE, a downlink control channelduring the monitored duration, wherein the downlink control channel isused for a downlink shared channel (DL-SCH); continuing monitoring thedownlink control channel if the downlink control channel is successfullydecoded by the UE during the monitored duration; and entering a DRX modeupon receiving a command message.
 2. The method of claim 1, wherein theRRC signaling indicates a length of the monitored duration.
 3. Themethod of claim 1, wherein the downlink control channel is a physicaldownlink control channel (PDCCH).
 4. The method of claim 1, furthercomprising inactivating the DRX mode if the downlink control channel issuccessfully decoded by the UE during the monitored duration.
 5. Themethod of claim 1, wherein the UE continues monitoring the downlinkcontrol channel while a timer is running.
 6. The method of claim 1,wherein the DRX period is applied to the UE while the DRX mode isapplied.
 7. A user equipment (UE) for monitoring a control channel in awireless communication system, the UE comprising: a receiver configuredfor receiving, from a network, information associated with adiscontinuous reception (DRX) period via a radio resource control (RRC)signaling, wherein the DRX period includes a monitored duration and anunmonitored duration; and a processor configured for: monitoring adownlink control channel during the monitored duration, wherein thedownlink control channel is used for a downlink shared channel (DL-SCH);continuing monitoring the downlink control channel if the downlinkcontrol channel is successfully decoded during the monitored duration;and entering a DRX mode upon receiving a command message.
 8. The userequipment of claim 7, wherein the RRC signaling indicates a length ofthe monitored duration.
 9. The user equipment of claim 7, wherein thedownlink control channel is a physical downlink control channel (PDCCH).10. The user equipment of claim 7, wherein the processor is furtherconfigured for monitoring the downlink control channel while a timer isrunning.
 11. A network entity in a wireless communication system, thenetwork entity comprising: a transmitter configured for: transmitting,to a user equipment (UE), information associated with a discontinuousreception (DRX) period via a radio resource control (RRC) signaling,wherein the DRX period includes a monitored duration and an unmonitoredduration; transmitting, to the UE, a control signal via a downlinkcontrol channel, wherein the downlink control channel is: monitored bythe UE during the monitored duration, used for a downlink shared channel(DL-SCH), and continuously monitored by the UE if the downlink controlchannel is successfully decoded by the UE during the monitored duration;and transmitting a command message to allow the UE to enter a DRX mode.12. The network entity of claim 11, wherein the RRC signaling indicatesa length of the monitored duration.
 13. The network entity of claim 11,wherein the downlink control channel is a physical downlink controlchannel (PDCCH).
 14. The network entity of claim 11, where the downlinkcontrol channel is continuously monitored by the UE while a timer isrunning.